This invention relates to apparatus for making fibrous webs, comprising a feeder for feeding a fibrous feed web tooth-carrying carding drums, which rotate in the same sense at such a surface velocity that carded fibers fly off the drum under centrifugal force, and a continuously moving, air-permeable collecting surface, which is subjected to suction and by which the fibers which fly away from each carding drum in a partial stream are successively received at locations which succeed each other in the direction of movement of the collecting surface.
Conventional carding apparatus comprises one carding drum and a plurality of working rollers for combing part of the fibers out of the fibrous material which is carried by the carding drum. Those fibers which have been entrained by the working rollers are removed from the latter and returned to the carding drums by clearing rollers. Whereas the working and clearing rollers open the fibrous material, the formation of a highly uniform fibrous web on the collecting surface was not ensured, particularly if the throughput of material was rather high. This was due to the fact that the fibers tend to ball together as they fly toward the collecting surface and this tendency increases with the number of fibers per unit of volume.
In order to avoid that disadvantage and to permit the making of a uniform fibrous web, it is already known from Austrian Pat. No. 325,996 to provide above the carding drum a second carding drum, which is fed with part of the fibers of the fibrous feed web. That part has been removed from the first carding drum by means of a working roller and a clearing roller. As a result, two partial streams of the fibers are received by the collecting surface at locations which succeed each other in the direction of movement of the collecting surface. As a result, the fiber density in each partial stream is reduced so that the fibers are more uniformly deposited on the collecting surface. Besides, the fibrous web is built up in two layers so that the doubling effect results in a higher uniformity even if there is an irregularity in one partial stream. Such irregularities in the resulting fibrous web are compensated at least in part by the formation of the second layer. In order to achieve a higher throughput of material and a still further uniformity, it would be desirable to divide the fibrous feed web into more than two partial streams. But that is not possible with the known apparatus. Besides, the transfer of part of the fibrous material from one carding drum to another by means of a pair of working and clearer rollers is expensive and such arrangement is liable to be deranged.